When I was little I used to love climbing up a eucalyptus tree in our backyard. I was forbidden (with good reason) from turning it into a real tree house, but I used to take my AM radio up there and pretend I was in my own little world. I'm sure there would be some danger in being exposed to the elements, but tents always get sticky and gross and an underground bunker is usually reserved for prisoners, mad men or people with guns so I'm going to hold off on that one for as long as possible.